Mark-
It's not the pulley, that's ridiculous. Even if it did wear away over time, that would not cause the occasional speed dips when out of quartz lock mode. Did the service manual actually suggest that? I would have suspected a bad belt before a pulley.
The problem you are having is because the electrolytic capacitors in the speed circuit have gone bad. I know this because the exact same thing happened to my T60 and T65C. I'm not sure if lack of use had anything to do with their degradation, in theory the electrolytic paste can dry out and depolarize if they sit around too long. But none of that matters now. The problem is fixable, I took care of my 2 units and now they run steady. I couldn't find a technician locally that would do the job reasonably, so I decided to do the job myself. The parts were cheap (less than $10) and as I was an electronics hobbyist as a kid, I was fortunate enough to have the skills.
A proper sized belt is also necessary, too loose and it slips, too tight and it pulls the platter towards the motor pulley.
The first thing I thought of when I saw your username was Wayside NJ. If that's where you live, I am nearby (Long Branch) and can give you a hand.
Good luck.
Rich